Some problems associated with pipes involve the difficulty of monitoring flows therethrough and pressures therein. In this respect, these measurements are interrelated in that flow through a pipe can often be determined by monitoring pressures in the pipe at various positions therealong. For this reason, in order to monitor pressure through pipe lines or strings pressure gauges spaced therealong are often used. Normally, pressure gauge assemblies are mounted on larger pipes, whose pressures are to be monitored, by pipe stands or stubs. That is, a hole is bored in a large pipe whose pressure is to be monitored, the hole is threaded, and thereafter, a small pipe stub having male threads at a mounting end and a pressure gauge on the opposite end is screwed into the hole. Pressure is transmitted to the pressure gauge via the pipe stub and the pressure gauges registers the pressure. A number of pressure sensors for use with pipe stubs are sold commercially. Most of these pressure sensores include a housing having a membrane mounted therein with a pressure inlet on one side of the membrane and a measuring outlet on the other side of the membrane. The pressure inlet normally has female threads for receiving male threads of the pipe stub described above and a narrow passage filled with a liquid is on the other side of the membrane. Movement of this liquid, such as oil, in the narrow passage causes movement of an indicator to monitor pressure in the larger pipe. Of course, pressure in the larger pipe causes movement of the membrane which, in turn, moves the liquid.
There are several difficulties often associated with the above described arrangement. When the pipe whose pressure is being measured is transporting a slurry, such as a coal slurry, solid particles therein tend to clog, or fill, gaps, or holes in the pipe. Thus, in many applications, the pipe stubs giving access to the membranes are clogged by solid or sticky substance thereby not allowing transmission of pressure to the membranes and causing the gauges to give improper readings. It is an object of this invention to provide a pipe pressure sensor which can be accurately used with pipes transporting slurries and which is not unduly subject to being clogged by solid, or sticky, substances. Some prior-art pipe pressure measuring devices of the type described above include purge ports and must be periodically purged with a pressurized fluid. It is an object of this invention to provide a pipe pressure sensor which can be used to measure pressures in slurry transporting pipes without needing to be periodically purged.
Yet another difficulty with the above-described prior art arrangement is that the small measuring passage located above the membrane often must be filled with oil. Such a thin passage is difficult to fill with oil without leaving air bubbles therein. In order to properly fill some gauges with oil, it is necessary to apply a vacuum to the passage. It is an object of this invention, to provide a pipe pressure sensor which can be filled with a liquid without the application of a vacuum.
In order to avoid the above-described clogging problems associated with pipe pressure gauges utilizing small pipe stubs, some pipe pressure gauges comprise pressure-sensing sections of pipes which are installed by cutting out a section from a pipe string and filling the gap left thereby with the pressure sensor pipe section. Some such pressure-sensor pipe sections have membranes extending about the entire inner surfaces of the substitute sections so that there is no hole which can become clogged prior to the membranes. Again movement of the membranes causes movement of liquid in passages on opposite side of the membranes. Although such pressure-measuring pipe sections are highly beneficial for small pipes, where it is easy to replace a section of pipe and where such a specialized section would not be unduly expensive, such a section is often not particularly practical for pipes whose diameters are greater than three inches. Several such pressure detectors are described in U.S. Pat. Nos. 4,534,224 to Raftis and 4,218,926 to DeVisser. It is an object of this invention to provide a pipe pressure sensor which can be easily and relatively inexpensively mounted on large diameter pipe strings but yet which does not involve the use of a pipe stub whose passage could get clogged.
A pipe pressure sensor has been suggested which is mounted to a pipe by boring a hole in the pipe, inserting a housing of a pressure gauge having a membrane mounted therein down through the hole, and welding the housing to the pipe. Such an arrangement has benefits, however, the housing still has an opening leading to a membrane which can become clogged. It is an object of this invention to provide a pipe pressure sensor which does not involve a passage leading to a pressure sensing membrane which can become clogged.
Many types of prior-art pipe pressure sensors can only be used with specific types of pipe. It is an object of this invention to provide a pipe pressure sensor which is not only inexpensive and satisfactorily accurate, but which can be used with various types of pipe includes both plastic and metal pipes.
Some prior art pressure sensors require discontinuities in the walls of pipes with which they are used. For example, some require holes in the walls of the pipes and some require protrusions in the walls of the pipes. Fluid flows through these pipes are disrupted by these discontinuities, thereby causing turbulence which can increase wear on pipe-string systems. It is an object of this invention, to provide a pipe pressure sensor which does not create a turbulence-creating discontinuity on the inner surface of a pipe whose pressure is being measured.
It is a further object of this invention to provide a pipe pressure sensor which is inexpensive to manufacture and install.